Conventionally, an image forming apparatus (image reading apparatus) such as a scanner, a copier, an MFP (multi-function peripheral) and the like, uses a lighting device and a lens array in which a plurality of lenses is arranged to form an image of a document on an image sensor and read the document image. Further, in an image forming apparatus such as a printer, a copier, an MFP (multi-function printer) and the like, using a light-emitting element such as LED and the lens array, light ray from the LED is imaged on a photoconductive drum through the lens array to form (expose) an image on the photoconductive drum. The lens array is constituted by combining a plurality of lenses with apertures.
However, if an optical axis between lenses through which a light ray passes deviates, the light ray enters into a lens or mirror of next element to generate stray light, and thus imaging property and light intensity variation of the lens array are greatly deteriorated. When a plurality of lenses and apertures are combined together, property of the lens array is deteriorated due to deviation at the time of assembly.
In Japanese Unexamined Patent Application Publication No. 2014-142449, an optical device (imaging element array) is disclosed in which lenses and mirrors are integrally molded to make deviation of the optical axis between the lens and the mirror small and a groove depth L of mirror surface is larger than a mirror width WO to reduce the stray light. However, as the groove depth L of mirror surface is larger than the mirror width WO, the flow of resin during molding is worse and molding time becomes long. Alternatively, there is a problem that width of protrusion to pitch is narrow to reduce optical efficiency.